Cholelithiasis, of which 80 percent are cholesterol gallstones, is one of the most common and expensive digestive diseases in the USA. The human disease is familial and heritable in part, but the genetic basis is unknown. It has been demonstrated that in inbred strains of mice, cholesterol gallstone formation is genetically determined, with two genes, Lith1 and Lith2, accounting for most of the difference in susceptibility between C57L and AKR strains. The applicant proposes to investigate the inbred mouse as an experimental model for human gallstone disease. The genetic background of the mouse provides powerful experimental opportunities, and a detailed knowledge of the phenotype is essential to clone the genes, identify the proteins and regulatory molecules, which should serve as targets for rational drug design and gallstone prevention. The applicant proposes to (i) characterize the biliary phenotypes of gallstone formation in inbred mice with high and low gallstone prevalence rates; (ii) determine alterations in hepatic/intestinal cholesterol and bile salt metabolism that account for cholesterol supersaturated bile; (iii) define the hepato-biliary phenotypes in reciprocal congenics of Lith1 and Lith2 to determine the effects of the individual genes; (iv) test the phenotype expression of "megalin", a candidate gene within the Lith1 locus that may control canalicular cholesterol transport; and (v) determine the role of de novo cholesterol synthesis in gallstone formation and prevention. These studies will be carried out in parallel with high- resolution genotype studies of the same mouse strains, crosses and congenics by Dr. Beverly Paigen at The Jackson Laboratory, thereby coupling genetic and functional analyses in understanding the pathophysiology of the disease. This work should pave the way for identifying the major Lith genes in humans, which, in turn, should lead to strategies for early diagnosis of the trait and rational approaches to prevention.